Some docs fixes for polls

[DA-344]

Summary

1st fix: Poll & PollMedia in docs

This is how it actually looks:

It it shown like it is a non-constructable class, when it is, same with discord.Poll.

And this is how it should look (using ForumTag as an example):

2nd fix: Missing dot in PollLayoutType & Poll.answers

Like... a missing dot.

3rd fix: Move PollAnswer to Discord Models

As PollAnswer is not meant to be user constructable it has been moved to Discord Models

4th fix: Make PollMedia have its own reference

Just makes PollMedia has its own reference... as said.

5th fix: Missing space in Poll docs

It is missing a space between "Default" and "to":

6th fix: poll being undocumented in InteractionResponse.send_message

Well... that.

I have not found further errors, so the PR is ready to be merged.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

[DA-344]

The PR is now ready for merging as I haven't found any further errors.